HP 5920 User manual

HP 5920 & 5900 Switch Series
IP Multicast
Configuration Guide
Part number: 5998-3373
Software version: Release2207
Document version: 6W100-20121130

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Contents
Multicast overview ······················································································································································· 1
Introduction to multicast····················································································································································1
Information transmission techniques·······················································································································1
Multicast features······················································································································································3
Common notations in multicast ·······························································································································4
Multicast benefits and applications ························································································································4
Multicast models································································································································································5
Multicast architecture························································································································································5
Multicast addresses ··················································································································································6
Multicast protocols ···················································································································································9
Multicast packet forwarding mechanism····················································································································· 11
Configuring IGMP snooping ·····································································································································13
Overview········································································································································································· 13
Basic concepts in IGMP snooping······················································································································· 13
How IGMP snooping works ································································································································· 15
Protocols and standards ······································································································································· 16
IGMP snooping configuration task list························································································································· 16
Configuring basic IGMP snooping functions ·············································································································· 17
Enabling IGMP snooping ····································································································································· 17
Specifying the IGMP snooping version··············································································································· 18
Setting the maximum number of IGMP snooping forwarding entries······························································ 18
Configuring parameters for IGMP queries and responses ··············································································· 18
Configuring IGMP snooping port functions················································································································· 19
Setting aging timers for dynamic ports ··············································································································· 19
Configuring static ports········································································································································· 20
Enabling IGMP snooping fast-leave processing································································································· 21
Configuring IGMP snooping policies··························································································································· 22
Configuring a multicast group filter····················································································································· 22
Configuring multicast source port filtering·········································································································· 22
Enabling dropping unknown multicast data······································································································· 23
Setting the maximum number of multicast groups on a port ············································································ 23
Enabling the multicast group replacement function ··························································································· 24
Displaying and maintaining IGMP snooping·············································································································· 25
IGMP snooping configuration examples ····················································································································· 25
Group policy configuration example ·················································································································· 25
Static port configuration example ······················································································································· 27
Troubleshooting IGMP snooping ·································································································································· 30
Layer 2 multicast forwarding cannot function ···································································································· 30
Multicast group filter does not work···················································································································· 30
Configuring multicast routing and forwarding·········································································································32
Overview········································································································································································· 32
RPF check mechanism ··········································································································································· 32
Static multicast routes············································································································································ 34
Multicast forwarding across unicast subnets ······································································································ 36
Configuration task list ···················································································································································· 36
Enabling IP multicast routing········································································································································· 37
Configuring multicast routing and forwarding············································································································ 37
Configuring static multicast routes······················································································································· 37

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Configuring the RPF route selection rule ············································································································· 37
Configuring multicast load splitting····················································································································· 38
Configuring a multicast forwarding boundary··································································································· 38
Configuring static multicast MAC address entries····························································································· 38
Displaying and maintaining multicast routing and forwarding················································································· 39
Configuration examples ················································································································································ 40
Changing an RPF route········································································································································· 40
Creating an RPF route··········································································································································· 42
Multicast forwarding over a GRE tunnel············································································································· 44
Troubleshooting multicast routing and forwarding····································································································· 47
Static multicast route failure ································································································································· 47
Multicast data fails to reach receivers················································································································· 48
Configuring IGMP······················································································································································49
Overview········································································································································································· 49
IGMPv1 overview·················································································································································· 49
IGMPv2 enhancements········································································································································· 50
IGMPv3 enhancements········································································································································· 51
Protocols and standards ······································································································································· 53
IGMP configuration task list ·········································································································································· 53
Configuring basic IGMP functions ······························································································································· 53
Enabling IGMP ······················································································································································ 53
Specifying the IGMP version································································································································ 54
Configuring an interface as a static member interface····················································································· 54
Configuring a multicast group filter····················································································································· 55
Adjusting IGMP performance ······································································································································· 55
Enabling IGMP fast-leave processing·················································································································· 55
Displaying and maintaining IGMP······························································································································· 56
IGMP configuration examples ······································································································································ 56
Network requirements··········································································································································· 56
Configuration procedure ······································································································································ 57
Verifying the configuration··································································································································· 58
Troubleshooting IGMP··················································································································································· 58
No membership information on the receiver-side router··················································································· 58
Inconsistent membership information on the routers on the same subnet························································ 59
Configuring PIM·························································································································································60
Overview········································································································································································· 60
PIM-DM overview ·················································································································································· 60
PIM-SM overview··················································································································································· 63
Administrative scoping overview························································································································· 68
Protocols and standards ······································································································································· 69
Configuring PIM-DM ······················································································································································ 70
PIM-DM configuration task list······························································································································ 70
Configuration prerequisites ·································································································································· 70
Enabling PIM-DM··················································································································································· 70
Enabling the state refresh feature ························································································································ 70
Configuring state refresh parameters·················································································································· 71
Configuring PIM-DM graft retry timer·················································································································· 71
Configuring PIM-SM······················································································································································· 72
PIM-SM configuration task list······························································································································ 72
Configuration prerequisites ·································································································································· 72
Enabling PIM-SM ··················································································································································· 72
Configuring an RP ················································································································································· 73
Configuring a BSR················································································································································· 74

iii
Configuring multicast source registration············································································································ 76
Configuring switchover to SPT ····························································································································· 77
Configuring common PIM features······························································································································· 77
Configuration task list ··········································································································································· 77
Configuration prerequisites ·································································································································· 78
Configuring a multicast data filter ······················································································································· 78
Configuring a hello message filter ······················································································································ 78
Configuring PIM hello message options ············································································································· 79
Configuring common PIM timers ························································································································· 80
Setting the maximum size of each join or prune message ··············································································· 82
Enabling PIM to work with BFD ··························································································································· 82
Displaying and maintaining PIM·································································································································· 82
PIM configuration examples ········································································································································· 83
PIM-DM configuration example ··························································································································· 83
PIM-SM non-scoped zone configuration example ····························································································· 86
PIM-SM admin-scoped zone configuration example························································································· 89
Troubleshooting PIM ······················································································································································ 94
A multicast distribution tree cannot be correctly built························································································ 94
Multicast data is abnormally terminated on an intermediate router ································································ 95
An RP cannot join an SPT in PIM-SM ·················································································································· 95
An RPT cannot be built or multicast source registration fails in PIM-SM·························································· 96
Configuring MLD snooping ·······································································································································97
Overview········································································································································································· 97
Basic concepts in MLD snooping························································································································· 97
How MLD snooping works ··································································································································· 99
Protocols and standards ·····································································································································100
MLD snooping configuration task list ·························································································································100
Configuring basic MLD snooping functions ··············································································································101
Enabling MLD snooping ·····································································································································101
Specifying the MLD snooping version···············································································································102
Setting the maximum number of MLD snooping forwarding entries······························································102
Configuring parameters for MLD queries and responses ···············································································103
Configuring MLD snooping port functions·················································································································103
Setting aging timers for dynamic ports ·············································································································104
Configuring static ports·······································································································································104
Enabling MLD snooping fast-leave processing·································································································105
Configuring MLD snooping policies···························································································································106
Configuring an IPv6 multicast group filter ········································································································106
Configuring IPv6 multicast source port filtering ·······························································································107
Enabling dropping unknown IPv6 multicast data ····························································································107
Setting the maximum number of IPv6 multicast groups on a port··································································108
Enabling the IPv6 multicast group replacement function·················································································108
Displaying and maintaining MLD snooping··············································································································109
MLD snooping configuration examples ·····················································································································110
IPv6 group policy configuration example·········································································································110
Static port configuration example ·····················································································································111
Troubleshooting MLD snooping ··································································································································114
Layer 2 multicast forwarding cannot function ··································································································114
IPv6 multicast group filter does not work··········································································································115
Configuring IPv6 multicast routing and forwarding ····························································································· 116
Overview·······································································································································································116
RPF check mechanism ·········································································································································116
IPv6 multicast forwarding across IPv6 unicast subnets····················································································118

iv
Configuration task list ··················································································································································118
Enabling IPv6 multicast routing···································································································································118
Configuring IPv6 multicast routing and forwarding ·································································································119
Configuring the RPF route selection rule ···········································································································119
Configuring IPv6 multicast load splitting···········································································································119
Configuring an IPv6 multicast forwarding boundary ······················································································119
Configuring IPv6 static multicast MAC address entries···················································································120
Displaying and maintaining IPv6 multicast routing and forwarding ······································································120
IPv6 multicast routing and forwarding configuration example ···············································································121
Network requirements·········································································································································121
Configuration procedure ····································································································································122
Verifying the configuration·································································································································123
Troubleshooting····························································································································································124
IPv6 multicast data fails to reach receivers·······································································································124
Configuring MLD····················································································································································· 125
Overview·······································································································································································125
How MLDv1 works··············································································································································125
MLDv2 enhancements·········································································································································127
Protocols and standards ·····································································································································128
MLD configuration task list ··········································································································································128
Configuring basic MLD functions ·······························································································································128
Enabling MLD ······················································································································································128
Specifying the MLD version································································································································129
Configuring an interface as a static member interface···················································································129
Configuring an IPv6 multicast group filter ········································································································130
Adjusting MLD performance ·······································································································································130
Enabling MLD fast-leave processing··················································································································130
Displaying and maintaining MLD·······························································································································131
MLD configuration examples ······································································································································131
Network requirements·········································································································································131
Configuration procedure ····································································································································132
Verifying the configuration·································································································································133
Troubleshooting MLD ···················································································································································133
No member information exists on the receiver-side router ·············································································133
Inconsistent membership information on the routers on the same subnet······················································134
Configuring IPv6 PIM·············································································································································· 135
PIM overview ································································································································································135
IPv6 PIM-DM overview········································································································································135
IPv6 PIM-SM overview ········································································································································138
IPv6 administrative scoping overview ···············································································································143
Protocols and standards ·····································································································································145
Configuring IPv6 PIM-DM············································································································································145
IPv6 PIM-DM configuration task list ···················································································································145
Configuration prerequisites ································································································································146
Enabling IPv6 PIM-DM ········································································································································146
Enabling the state refresh feature ······················································································································146
Configuring state refresh parameters················································································································147
Configuring IPv6 PIM-DM graft retry timer ·······································································································147
Configuring IPv6 PIM-SM ············································································································································148
IPv6 PIM-SM configuration task list····················································································································148
Configuration prerequisites ································································································································148
Enabling IPv6 PIM-SM·········································································································································148
Configuring an RP ···············································································································································149

v
Configuring a BSR···············································································································································150
Configuring IPv6 multicast source registration ·································································································152
Configuring switchover to SPT ···························································································································153
Configuring common IPv6 PIM features ····················································································································153
Configuration task list ·········································································································································153
Configuration prerequisites ································································································································153
Configuring an IPv6 multicast data filter···········································································································153
Configuring a hello message filter ····················································································································154
Configuring IPv6 PIM hello message options···································································································154
Configuring common IPv6 PIM timers ···············································································································156
Setting the maximum size of each join or prune message ·············································································157
Enabling IPv6 PIM to work with BFD·················································································································157
Displaying and maintaining IPv6 PIM························································································································158
IPv6 PIM configuration examples ·······························································································································159
IPv6 PIM-DM configuration example·················································································································159
IPv6 PIM-SM non-scoped zone configuration example···················································································162
IPv6 PIM-SM admin-scoped zone configuration example···············································································165
Troubleshooting IPv6 PIM············································································································································170
A multicast distribution tree cannot be correctly built······················································································170
IPv6 multicast data is abnormally terminated on an intermediate router ······················································171
An RP cannot join an SPT in IPv6 PIM-SM········································································································172
An RPT cannot be built or IPv6 multicast source registration fails in IPv6 PIM-SM·······································172
Support and other resources ·································································································································· 174
Contacting HP ······························································································································································174
Subscription service ············································································································································174
Related information······················································································································································174
Documents····························································································································································174
Websites·······························································································································································174
Conventions ··································································································································································175
Index ········································································································································································ 177

1
Multicast overview
Introduction to multicast
As a technique that coexists with unicast and broadcast, the multicast technique effectively addresses the
issue of point-to-multipoint data transmission. By enabling high-efficiency point-to-multipoint data
transmission over a network, multicast greatly saves network bandwidth and reduces network load.
By using multicast technology, a network operator can easily provide new value-added services, such as
live webcasting, web TV, distance learning, telemedicine, web radio, real-time video conferencing, and
other bandwidth-critical and time-critical information services.
Information transmission techniques
The information transmission techniques include unicast, broadcast, and multicast.
Unicast
In unicast transmission, the information source must send a separate copy of information to each host that
needs the information.
Figure 1 Unicast transmission
In Figure 1, assume that Host B, Host D and Host E need the information. A separate transmission channel
must be established from the information source to each of these hosts.
In unicast transmission, the traffic transmitted over the network is proportional to the number of hosts that
need the information. If a large number of hosts need the information, the information source must send
a separate copy of the same information to each of these hosts. Sending many copies can place a
tremendous pressure on the information source and the network bandwidth.
Source
Receiver
Receiver
Receiver
Host A
Host B
Host C
Host D
Host E
Packets for Host B
Packets for Host D
Packets for Host E
IP network

2
Unicast is not suitable for batch transmission of information.
Broadcast
In broadcast transmission, the information source sends information to all hosts on the subnet, even if
some hosts do not need the information.
Figure 2 Broadcast transmission
In Figure 2, assume that only Host B, Host D, and Host E need the information. If the information is
broadcast to the subnet, Host A and Host C also receive it. In addition to information security issues,
broadcasting to hosts that do not need the information also causes traffic flooding on the same subnet.
Broadcast is not as efficient as multicast for sending data to groups of hosts.
Multicast
Unicast and broadcast techniques cannot provide point-to-multipoint data transmissions with the
minimum network consumption.
Multicast transmission can solve this problem. When some hosts on the network need multicast
information, the information sender, or multicast source, sends only one copy of the information.
Multicast distribution trees are built through multicast routing protocols, and the packets are replicated
only on nodes where the trees branch.

3
Figure 3 Multicast transmission
The multicast source sends only one copy of the information to a multicast group. Host B, Host D, and
Host E, which are information receivers, must join the multicast group. The routers on the network
duplicate and forward the information based on the distribution of the group members. Finally, the
information is correctly delivered to Host B, Host D, and Host E.
To summarize, multicast has the following advantages:
•Advantages over unicast—Because multicast traffic flows to the farthest-possible node from the
source before it is replicated and distributed, an increase in the number of hosts does not increase
the load of the source or remarkably add to the usage of network resources.
•Advantages over broadcast—Because multicast data is sent only to the receivers that need it,
multicast uses network bandwidth reasonably and enhances network security. In addition, data
broadcast is confined to the same subnet, but multicast is not.
Multicast features
•A multicast group is a multicast receiver set identified by an IP multicast address. Hosts must join a
multicast group to become members of the multicast group before they receive the multicast data
addressed to that multicast group. Typically, a multicast source does not need to join a multicast
group.
•An information sender is called a "multicast source." A multicast source can send data to multiple
multicast groups at the same time, and multiple multicast sources can send data to the same
multicast group at the same time.
•The group memberships are dynamic. Hosts can join or leave multicast groups at any time.
Multicast groups are not subject to geographic restrictions.
•Routers or Layer 3 switches that support Layer 3 multicast are called "multicast routers" or "Layer 3
multicast devices." In addition to providing the multicast routing function, a multicast router can also
manage multicast group memberships on stub subnets with attached group members. A multicast
router itself can be a multicast group member.

4
For a better understanding of the multicast concept, you can compare multicast transmission to the
transmission of TV programs.
Table 1 Comparing TV program transmission and multicast transmission
TV program transmission Multicast transmission
A TV station transmits a TV program through a
channel.
A multicast source sends multicast data to a multicast
group.
A user tunes the TV set to the channel. A receiver joins the multicast group.
The user starts to watch the TV program transmitted
by the TV station on the channel.
The receiver starts to receive the multicast data that the
source is sending to the multicast group.
The user turns off the TV set or tunes to another
channel.
The receiver leaves the multicast group or joins another
group.
Common notations in multicast
The following notations are commonly used in multicast transmission:
•(*, G)—Rendezvous point tree (RPT), or a multicast packet that any multicast source sends to
multicast group G. The asterisk (*) represents any multicast source, and "G" represents a specific
multicast group.
•(S, G)—Shortest path tree (SPT), or a multicast packet that multicast source "S" sends to multicast
group "G." "S" represents a specific multicast source, and "G" represents a specific multicast
group.
For more information about the concepts RPT and SPT, see "Configuring PIM"and "Configuring IPv6
PIM."
Multicast benefits and applications
Multicast benefits
•Enhanced efficiency—Reduces the processor load of information source servers and network
devices.
•Optimal performance—Reduces redundant traffic.
•Distributed application—Enables point-to-multipoint applications at the price of minimum network
resources.
Multicast applications
•Multimedia and streaming applications, such as web TV, web radio, and real-time video/audio
conferencing
•Communication for training and cooperative operations, such as distance learning and
telemedicine
•Data warehouse and financial applications (stock quotes)
•Any other point-to-multipoint application for data distribution

5
Multicast models
Based on how the receivers treat the multicast sources, the multicast models include any-source multicast
(ASM), source-filtered multicast (SFM), and source-specific multicast (SSM).
ASM model
In the ASM model, any sender can send information to a multicast group as a multicast source, and
receivers can join a multicast group identified by a group address and get multicast information
addressed to that multicast group. In this model, receivers do not know the positions of the multicast
sources in advance. However, they can join or leave the multicast group at any time.
SFM model
The SFM model is derived from the ASM model. To a sender, the two models appear to have the same
multicast membership architecture.
The SFM model functionally extends the ASM model. The upper-layer software checks the source address
of received multicast packets and permits or denies multicast traffic from specific sources. Therefore,
receivers can receive the multicast data from only part of the multicast sources. To a receiver, multicast
sources are not all valid, but are filtered.
SSM model
Users might be interested in the multicast data from only certain multicast sources. The SSM model
provides a transmission service that enables users to specify at the client side the multicast sources in
which they are interested.
The main difference between the SSM model and the ASM model is that in the SSM model, receivers
have already determined by some other means the locations of the multicast sources. In addition, the
SSM model uses a multicast address range that is different from the ASM/SFM model. Dedicated
multicast forwarding paths are established between receivers and the specified multicast sources.
Multicast architecture
IP multicast addresses the following issues:
•Where should the multicast source transmit information to? (Multicast addressing.)
•What receivers exist on the network? (Host registration.)
•Where is the multicast source that will provide data to the receivers? (Multicast source discovery.)
•How should information be transmitted to the receivers? (Multicast routing.)
IP multicast is an end-to-end service. The multicast architecture involves the following parts:
•Addressing mechanism—A multicast source sends information to a group of receivers through a
multicast address.
•Host registration—Receiver hosts can join and leave multicast groups dynamically. This mechanism
is the basis for management of group memberships.
•Multicast routing—A multicast distribution tree (a forwarding path tree for multicast data on the
network) is constructed for delivering multicast data from a multicast source to receivers.
•Multicast applications—A software system that supports multicast applications, such as video
conferencing, must be installed on multicast sources and receiver hosts. The TCP/IP stack must
support reception and transmission of multicast data.

6
Multicast addresses
IP multicast addresses
•IPv4 multicast addresses:
IANA assigned the Class D address block (224.0.0.0 to 239.255.255.255) to IPv4 multicast.
Table 2 Class D IP address blocks and description
Address block Description
224.0.0.0 to 224.0.0.255
Reserved permanent group addresses. The IP address 224.0.0.0 is
reserved. Other IP addresses can be used by routing protocols and
for topology searching, protocol maintenance, and so on. Table 3
lists common permanent group addresses. A packet destined for an
address in this block will not be forwarded beyond the local subnet
regardless of the TTL value in the IP header.
224.0.1.0 to 238.255.255.255
Globally scoped group addresses. This block includes the following
types of designated group addresses:
•232.0.0.0/8—SSM group addresses.
•233.0.0.0/8—Glop group addresses.
239.0.0.0 to 239.255.255.255
Administratively scoped multicast addresses. These addresses are
considered locally unique rather than globally unique. You can
reuse them in domains administered by different organizations
without causing conflicts. For more information, see RFC 2365.
NOTE:
"Glop" is a mechanism for assigning multicast addresses between different ASs. By filling an AS numbe
r
into the middle two bytes of 233.0.0.0, you get 255 multicast addresses for that AS. For more
information, see RFC 2770.
Table 3 Some reserved multicast addresses
Address Description
224.0.0.1 All systems on this subnet, including hosts and routers.
224.0.0.2 All multicast routers on this subnet.
224.0.0.3 Unassigned.
224.0.0.4 DVMRP routers.
224.0.0.5 OSPF routers.
224.0.0.6 OSPF designated routers and backup designated routers.
224.0.0.7 Shared Tree (ST) routers.
224.0.0.8 ST hosts.
224.0.0.9 RIPv2 routers.
224.0.0.11 Mobile agents.
224.0.0.12 DHCP server/relay agent.
224.0.0.13 All Protocol Independent Multicast (PIM) routers.

7
Address Description
224.0.0.14 RSVP encapsulation.
224.0.0.15 All Core-Based Tree (CBT) routers.
224.0.0.16 Designated SBM.
224.0.0.17 All SBMs.
224.0.0.18 VRRP.
•IPv6 multicast addresses:
Figure 4 IPv6 multicast format
The following describes the fields of an IPv6 multicast address:
{0xFF—The most significant eight bits are 11111111, which indicates that this address is an IPv6
multicast address.
{Flags—The Flags field contains four bits.
Figure 5 Flags field format
Table 4 Flags field description
Bit Descri
p
tion
0 Reserved, set to 0.
R
•When set to 0, it indicates that this address is an IPv6 multicast
address without an embedded RP address.
•When set to 1, it indicates that this address is an IPv6 multicast
address with an embedded RP address. (The P and T bits must
also be set to 1.)
P
•When set to 0, it indicates that this address is an IPv6 multicast
address not based on a unicast prefix.
•When set to 1, it indicates that this address is an IPv6 multicast
address based on a unicast prefix. (The T bit must also be set to
1. )
T
•When set to 0, it indicates that this address is an IPv6 multicast
address permanently-assigned by IANA.
•When set to 1, it indicates that this address is a transient, or
dynamically assigned IPv6 multicast address.
{Scope—The Scope field contains four bits, which indicate the scope of the IPv6 internetwork for
which the multicast traffic is intended.

8
Table 5 Values of the Scope field
Value Meanin
g
0, F Reserved.
1 Interface-local scope.
2 Link-local scope.
3 Subnet-local scope.
4 Admin-local scope.
5 Site-local scope.
6, 7, 9 through D Unassigned.
8 Organization-local scope.
E Global scope.
{Group ID—The Group ID field contains 112 bits. It uniquely identifies an IPv6 multicast group in
the scope that the Scope field defines.
Ethernet multicast MAC addresses
•IPv4 multicast MAC addresses:
As defined by IANA, the most significant 24 bits of an IPv4 multicast MAC address are 0x01005E.
Bit 25 is 0, and the other 23 bits are the least significant 23 bits of a multicast IPv4 address.
Figure 6 IPv4-to-MAC address mapping
The most significant four bits of a multicast IPv4 address are 1110. Only 23 bits of the remaining
28 bits are mapped to a MAC address, so five bits of the multicast IPv4 address are lost. As a result,
32 multicast IPv4 addresses map to the same IPv4 multicast MAC address. Therefore, a device
might receive some unwanted multicast data at Layer 2 processing, which needs to be filtered by
the upper layer.
•IPv6 multicast MAC addresses:
As defined by IANA, the most significant 16 bits of an IPv6 multicast MAC address are 0x3333
as its address prefix. The least significant 32 bits are the least significant 32 bits of a multicast IPv6
address and are mapped to the remaining IPv6 multicast MAC address, so the problem of
duplicate IPv6-to-MAC address mapping also arises like IPv4-to-MAC address mapping.

9
Figure 7 An example of IPv6-to-MAC address mapping
IMPORTANT:
Because of the duplicate mapping from multicast IP address to multicast MAC address, the device mi
g
ht
inadvertently send multicast protocol packets as multicast data in Layer 2 forwardin
g
. To avoid this, do no
t
use the IP multicast addresses that are mapped to multicast MAC addresses 0100-5E00-00xx and
3333-0000-00xx (where "x" specifies any hexadecimal number from 0 to F).
Multicast protocols
Multicast protocols fall into the following categories:
•Layer 3 and Layer 2 multicast protocols:
{Layer 3 multicast refers to IP multicast working at the network layer.
Layer 3 multicast protocols—IGMP, MLD, PIM, IPv6 PIM, MSDP, MBGP, and IPv6 MBGP.
{Layer 2 multicast refers to IP multicast working at the data link layer.
Layer 2 multicast protocols—IGMP snooping, MLD snooping, PIM snooping, IPv6 PIM
snooping, multicast VLAN, and IPv6 multicast VLAN.
•IPv4 and IPv6 multicast protocols:
{For IPv4 networks—IGMP snooping, PIM snooping, multicast VLAN, IGMP, PIM, MSDP, and
MBGP.
{For IPv6 networks—MLD snooping, IPv6 PIM snooping, IPv6 multicast VLAN, MLD, IPv6 PIM,
and IPv6 MBGP.
This section provides only general descriptions about applications and functions of the Layer 2 and Layer
3 multicast protocols in a network. For more information about these protocols, see the related chapters.
NOTE:
Currently, the switches support IGMP snooping, MLD snooping, IGMP, MLD, PIM, and IPv6 PIM.
Layer 3 multicast protocols
Layer 3 multicast protocols include multicast group management protocols and multicast routing
protocols.

10
Figure 8 Positions of Layer 3 multicast protocols
•Multicast group management protocols:
Typically, the Internet Group Management Protocol (IGMP) or Multicast Listener Discovery (MLD)
protocol is used between hosts and Layer 3 multicast devices that directly connect to the hosts to
define how to establish and maintain their multicast group memberships.
•Multicast routing protocols:
A multicast routing protocol runs on Layer 3 multicast devices to establish and maintain multicast
routes and correctly and efficiently forward multicast packets. Multicast routes constitute loop-free
data transmission paths (also known as multicast distribution trees) from a data source to multiple
receivers.
In the ASM model, multicast routes include intra-domain routes and inter-domain routes.
{An intra-domain multicast routing protocol discovers multicast sources and builds multicast
distribution trees within an AS to deliver multicast data to receivers. Among a variety of mature
intra-domain multicast routing protocols, PIM is most widely used. Based on the forwarding
mechanism, PIM has dense mode (often referred to as "PIM-DM") and sparse mode (often
referred to as "PIM-SM").
{An inter-domain multicast routing protocol is used for delivering multicast information between
two ASs. So far, mature solutions include Multicast Source Discovery Protocol (MSDP) and
MBGP. MSDP propagates multicast source information among different ASs. MBGP is an
extension of the MP-BGP for exchanging multicast routing information among different ASs.
For the SSM model, multicast routes are not divided into intra-domain routes and inter-domain
routes. Because receivers know the position of the multicast source, channels established through
PIM-SM are sufficient for the transport of multicast information.
Layer 2 multicast protocols
Layer 2 multicast protocols include IGMP snooping, MLD snooping, PIM snooping, IPv6 PIM snooping,
multicast VLAN, and IPv6 multicast VLAN.

11
Figure 9 Positions of Layer 2 multicast protocols
•IGMP snooping and MLD snooping:
IGMP snooping and MLD snooping are multicast constraining mechanisms that run on Layer 2
devices. They manage and control multicast groups by monitoring and analyzing IGMP or MLD
messages exchanged between the hosts and Layer 3 multicast devices, effectively controlling the
flooding of multicast data in a Layer 2 network.
•PIM snooping and IPv6 PIM snooping:
PIM snooping and IPv6 PIM snooping run on Layer 2 devices. They determine which ports are
interested in multicast data by analyzing the received IPv6 PIM messages, and add the ports to a
multicast forwarding entry to make sure multicast data can be forwarded to only the ports that are
interested in the data.
•Multicast VLAN and IPv6 multicast VLAN:
In the traditional multicast-on-demand mode, when users in different VLANs on a Layer 2 device
need multicast information, the upstream Layer 3 device must forward a separate copy of the
multicast data to each VLAN of the Layer 2 device. When the multicast VLAN or IPv6 multicast
VLAN feature is enabled on the Layer 2 device, the Layer 3 multicast device sends only one copy
of multicast to the multicast VLAN or IPv6 multicast VLAN on the Layer 2 device. This approach
avoids waste of network bandwidth and extra burden on the Layer 3 device.
Multicast packet forwarding mechanism
In a multicast model, a multicast source sends information to the host group identified by the multicast
group address in the destination address field of IP multicast packets. To deliver multicast packets to
receivers located at different positions of the network, multicast routers on the forwarding paths usually
need to forward multicast packets that an incoming interface receives to multiple outgoing interfaces.
Compared to a unicast model, a multicast model is more complex in the following aspects:
•To ensure multicast packet transmission in the network, unicast routing tables, routing tables for
multicast (for example, the MBGP routing table), and static multicast routes must be used as
guidance for multicast forwarding.
•To process the same multicast information from different peers received on different interfaces of the
same device, every multicast packet undergoes a reverse path forwarding (RPF) check on the

12
incoming interface. The RPF check result determines whether the packet will be forwarded or
discarded. The RPF check mechanism is the basis for most multicast routing protocols to implement
multicast forwarding.
For more information about the RPF mechanism, see "Configuring multicast routing and
forwarding"and "Configuring IPv6 multicast routing and forwarding."

13
Configuring IGMP snooping
Overview
IGMP snooping enables Layer 2 switches to establish a Layer 2 multicast forwarding table instead of
flooding all multicast packets. To populate the Layer 2 multicast forwarding table, IGMP snooping listens
to IGMP messages exchanged between a Layer 3 multicast device and hosts.
As shown in Figure 10, without IGMP snooping enabled, the Layer 2 switch floods multicast packets to
all devices. With IGMP snooping enabled, the Layer 2 switch forwards multicast packets of known
multicast groups to only the receivers that require the data at Layer 2. This feature improves bandwidth
efficiency, enhances multicast security, and helps per-host accounting for multicast users.
Figure 10 Multicast packet transmission without and with IGMP snooping
Basic concepts in IGMP snooping
IGMP snooping related ports
As shown in Figure 11, IGMP snooping runs on Switch A and Switch B, and Host A and Host C are
receiver hosts as members of a multicast group.